Signaling circuit



y 1944- c. D. HANSCOM SIGNALING CIRCUIT Filed Dec. 25, 1941 INVENTO/Q Byc. [2. HANSCOM I Patented May 2, 1944 2,347,777 SIGNALING omcmr ClarenceD. Hansoom, Denville, N. J., asslznor to Bell Telephone laboratories,Incorporated, New York, N. Y., a corporation of New York ApplicationDecember 23, 1941, Serial No. 424,100

4 Claims. (Cl. 177-380) This invention relates'to signaling systems andhas for its object an improved control of timed signaling.

Heretofore, in controlling the time of application of signaling current,it has been necessary to open the signaling circuit in order toterminate the signal. The consequent damage to the contact sat which theinterruption takes place has necessitated the use of precious metalcontacts, thereby increasing the cost of such control circuits.

In accordance with the present invention a signal may be terminated byincluding in the signaling circuit a transformer having a core of amagnetic alloy, the Curie point of which is slightly above roomtemperature, and heating then transformer to a temperature above theCurie D t.

The invention will be more clearly understood from a consideration ofthe following description in connection with the drawing in which:

Fig. 1 shows the essentials of the invention; while Fig. 2 shows theinvention together with certain typical control circuits.

It is known that materials such a iron or nickel, when heated, reach atemperature at which they become nonmagnetic. This temperature, known asthe Curie point, is fixed for the material, being, for example, 350 C.for pure nickel. However, in the case of magnetic alloys, it has beenfound that by varying the proportions of the components, an alloy may beobtained having a Curie point slightly above room temperature.

Referring to Fig. 1, transformer l is formed with a core 2 of a magneticalloy having a Curie point slightly above room temperature. Thesecondary winding 3 of the transformer is connected to conductors 4 and5 leading to a distant point where a signal represented by relay 6 isconnected to conductors I and 5. Relay 6 controls an obvious circuit foran indicator such as lamp 1.

When key 8 is operated, signaling current from source 9 is connected tothe primary winding I0 of transformer l Signaling current is thereupontransmitted by means of the transformer to the conductors 4 and 5operating signal 6.

At the same time an obvious circuit is closed for heating element ll.This element is so arranged with relation to transformer l and isselected to have such heating properties that the core 2 will reach itsCurie point in the desired length of time. When the Curie point isreached, the permeability of core 2 drops to a very low value, thecurrent induced in the secondary winding 3 of the transformer I becomesnegligible and signal 6 releases. Therefore it is possible transmit asignal of fixed duration without opening the signal circuit to mark theend of the desired'duraion. I

In Fig. 2 are shown typical circuitsby which the invention may be usedin a telephone system. Conductors 20, 2|, 22 and 23 represent incomingand outgoing sections of a trunk circuit, connected over back contactsof relay 24. When it is desired to transmit a signal over conductors 22and 23, key 25 is closed, completing obvious circuits for relays 24 and26. Relay 28 connects signaling source 21 to the primary winding oftransformer 28 and also completes a circuit for heater 2!. Relay 24 inoperating connectsthe secondary winding of transformer 28 to conductors22 and 23 and closes a locking circuit for relay 28. With the core oftransformer 28 at room temperature, signaling current is transmittedthrough the secondary winding of transformer 28 to conductors 22 and 23and relay 3c is energized to provide a holding circuit for relay 24.Ordinarily key 25 is operated only briefly, the signaling circuit beingheld under the control of relay 30 but no harm is done if the key isheld. When the core of transformer 28 reaches its Curie point, thesignaling current disappears from the secondary winding, terminating thesignal, and relay 30 releases. If key 25 has been released, relays 2|and 26 in turn release. The release or relay 24 recloses the talkingcircuit while the release of relay 28 opens the primary circuit oftransformer 28 and the circuit of heater 29.

By this arrangement the relay contacts in the talking circuit do notopen while the signaling current is passing over them and are thereforeprotected from damage. Therefore the contact metal need not be of asexpensive 2. type as would otherwise be required. In addition thereduction of the permeability of the core of transformer 28 also reducesthe inductive discharge when the primary circuit of the transformer isopened, also reducing the wear on these contacts.

In general, the permeability of a core may be restored by the naturalforces of radiation and convection, but assuming speedy restoration isimportant, relay 26 is shown to actuate artificial cooling means, suchas fan 32.

What is claimed is:

1. In a signaling system, means for transmitting a signal of definiteduration comprising a signaling source, a receiving circuit, a repeatingcoil connecting said source to said circuit, the core of current to opensaid contacts to said coil made of an alloy having a Curie pointslightly above room temperature, means for automatically arresting thetransmission of current from said source to said circuit comprisingmeans for heating said core to said Curie point to terminate said signaland means for simultaneously starting said signaling and said heatingoperation.

2. In a signaling system, a source of signaling current, a receivingcircuit, means or connecting said signaling current from said source tosaid circuit including a repeating coil and one or more contacts, meansfor arresting the transmission of current from said source to saidcircuit prior to opening said contacts comprising a core for saidrepeating coil having a Curie point above room temperature and means forheating said core to said Curie point, means for simultaneously startingsaid signaling and said heating operation and means eflective inresponse to the removal or said disconnect said source from saidcircuit.

3. In a signaling system, means for transmitting a signll oi definiteduration comprising a signaling source, a receiving circuit, a repeatingcoil connecting said source to said circuit, the

core of said coil made of an alloy having. a Curie point slightly aboveroom temperature, means ior automatically arresting the transmission ofcurrent from said source to said circuit comprising means for heatingsaid core to said Curie point to terminate said signal means forsimultaneously starting said signaling and said heating operation, andmeans responsive to the termination of said signal to restore thetemperature of said core.

4. In a signaling system, a source of signaling current, a receivingcircuit, means ior connecting said signaling current from said source tosaid circuit including a repeating coil and one or more contacts, meansfor arresting the transmission of current from said source to saidcircuit prior to opening said contacts comprising a core for said havinga Curie point above room temperature and means for heating said core tosaid Curie point, means for simultaneously starting said signaling andsaid heating operation, means eiiective in response to the removal orsaid current to open said contacts to disconnect said source from saidcircuit, and means to restore the temperature of said core.

CE D. KANSCOM.

